Role of carboxylic organic molecules in interfibrillar collagen mineralization

Abstract

Bone is a composite material made up of inorganic and organic counterparts. Most of the inorganic counterpart accounts for calcium phosphate (CaP) whereas the major organic part is composed of collagen. The interfibrillar mineralization of collagen is an important step in the biomineralization of bone and tooth. Studies have shown that synthetic CaP undergoes auto-transformation to apatite nanocrystals before entering the gap zone of collagen. Also, the synthetic amorphous calcium phosphate/collagen combination alone is not capable of initiating apatite nucleation rapidly. Therefore, it was understood that there is the presence of a nucleation catalyst obstructing the auto-transformation of CaP before entering the collagen gap zone and initiating rapid nucleation after entering the collagen gap zone. Therefore, studies were focused on finding the nucleation catalyst responsible for the regulation of interfibrillar collagen mineralization. Organic macromolecules and low-molecular-weight carboxylic compounds are predominantly present in the bone and tooth. These organic compounds can interact with both apatite and collagen. Adsorption of the organic compounds on the apatite nanocrystal governs the nucleation, crystal growth, lattice orientation, particle size, and distribution. Additionally, they prevent the auto-transformation of CaP into apatite before entering the interfibrillar compartment of the collagen fibril. Therefore, many carboxylic organic compounds have been utilized in developing CaP. In this review, we have covered different carboxylate organic compounds governing collagen interfibrillar mineralization.

New Nano-Crystalline Hydroxyapatite-Polycarboxy/Sulfo Betaine Hybrid Materials: Synthesis and Characterization

“…In the same line, the data obtained from the characterization of the HA mineral phase by XRD, TEM and FT-IR for the PCB hybrid material show a smaller HA mineral phase and less crystallinity compared to the other two materials. In this connection, it is well known that carboxylic groups containing organic compounds are known to regulate the nucleation and crystallization of hydroxyapatite in natural hard tissues [ 52 ].…”

Hydroxyapatite as a Material for Transplantology: Clinical Experience and Prospects of Application

“…When a solubility threshold is reached, micropackages of amorphous calcium phosphate or Posner clusters with the probable formula Ca9(PO4)6 are precipitated, which are thought to be stabilized by an organic component, the so-called "Howard factor." Further release of amorphous calcium phosphate can occur in two ways: by direct transport directly across the mitochondrial membrane or by reverse phagocytosis [9].…”

“…Collagen fibrils act as an organizing component in the formation of growth centers of hydroxyapatite crystals [9,15]. The initiation of hydroxyapatite crystals formation depends on amino acid patterns, in particular, the triplet of amino acids glycine-proline-hydroxyproline, which is the dominant motif of tropocollagen.…”

Amorphous Calcium Phosphate and Amorphous Calcium Phosphate Carboxylate: Synthesis and Characterization

“…Compared to noncollagenous proteins, small organic molecules such as citrate provide more carboxylic for calcium binding . However, less consideration has been given to incorporating COO – -containing small organic molecules in calcium phosphate (CaP), although their role was indicated in numerous postulated biomineralization . ACP and octa-calcium phosphate (OCP) are precursor phases that gradually crystallize to apatite .…”

“… 7 However, less consideration has been given to incorporating COO – -containing small organic molecules in calcium phosphate (CaP), although their role was indicated in numerous postulated biomineralization. 8 ACP and octa-calcium phosphate (OCP) are precursor phases that gradually crystallize to apatite. 9 Therefore, crystal growth, nucleation, and stabilization of apatite may be regulated by incorporating COO – in ACP or OCP.…”